Trowels are known which are useful for spreading flowable material into a flat sheet-like layer. Such operation is desirable, for example, in spreading underlayment onto a floor having surface irregularities so that the irregularities are filled and the top of the spread layer is substantially flat to receive an overlying floor covering in sheet or tile form. When the underlayment has been smoothed and permitted to harden, a layer of adhesive is usually applied over it and smoothed with a trowel; the floor covering is then laid over the adhesive, which upon hardening cements the floor covering to the underlayment layer.
In its simplest form, a conventional trowel comprises a handle and a flat blade to one side of which the handle is directly attached; the edge of the blade may be used to move around masses of the flowable material for general positioning of it, and the flat surface opposite the handle may be held more or less flat against the top of the layer of flowable material and moved about in lateral directions to effect smoothing of its exposed surface.
It is known to provide, along one or more edges of the trowel plate, one or more rows of serrations, so that by pressing such an edge downward through the flowable material to the substrate on which it rests, and then dragging the blade horizontally in a direction at right angles to the row of serrations, a multi-ridged layer of flowable material is formed having a uniform maximum thickness equal to the depth of the serrations. By thereafter dragging a plain edge of the blade across the ridges, a smooth uniform layer can be obtained.
Trowels are also known in which the blade holder comprises a rail extending along one face of the blade, to which rail a handle is secured or with which the handle is integral. In some cases the rail extends laterally beyond the handle grip, and it is also known to use a stiffening plate between handle and blade, which plate extends not only longitudinally but also laterally beyond the handle.
In addition, trowels are known in which the blade can be removed for cleaning or exchange, and the same or a new blade re-mounted on the blade holder. In some cases this has been accomplished by providing a mortise on the underside of the rail and a tenon on top of the blade so that the two can be joined or taken apart by a mutual sliding action. This of course requires that a special blade-and-tenon structure be provided.
It is also known to provide the blade with a longitudinal row of keyhole-shaped openings, and to provide a corresponding row of headed bolts on the underside of the rail, the heads fitting through the larger parts of the keyhole but being trapped when the stems of the screws are slid into the smaller parts of the keyholes, after which a screw is tightened to mount the blade tightly on the handle, as shown in U.S. Pat. No. 3,916,472 of W. E. Carder, filed Jan. 29, 1974 and issued Nov. 4, 1975. Such an arrangement, however, uses a complex array of screws, requires a special tightening step, and locates screw heads on the exposed side of the plate where they can interfere with the smoothing action.
While these various types of trowels are useful for many purposes, they leave something to be desired with respect to one or more of the characteristics of ease of removal and installation of the blade, simplicity of construction of those parts involved in such removal and installation, the degree and distribution of stiffness and flexibility of the blade, and smoothness of the levelling action.
Accordingly, an object of this invention is to provide a new and useful trowel assembly.
Another object is to provide such a trowel assembly in which the blade is especially easily removed from and attached to the blade holder, using a simple, inexpensive but reliable construction to accomplish this.
A further object is to provide such a trowel in which the distribution of stiffness and flexibility is especially well adapted to spreading a flat layer of flowable material over a substrate having irregularities in its surface.
A still further object is to provide such a trowel in which the tendency of the trowel to produce swirls in the material being spread by the trowel is mitigated.